There’s a new trend in agriculture called vertical farming. As humans learned to farm, we arranged plants outside in horizontal fields, and invented irrigation and fertilizer to grow bumper crops. But with modern technology and farmers’ cleverness, we can now stack those fields vertically, just as we stacked housing to make apartment buildings. Moving plants indoors has many benefits: Plants are not at the mercy of weather, less wilderness is cleared for farmland, and it’s easier to control the runoff of fertilizer and pesticides. But the choice of lighting can make or break the cost of a vertical farm and affect how long it might take for urban agriculture to blossom.